The present invention relates to X-ray computerized tomography (hereinafter abbreviated to xe2x80x9cCTxe2x80x9d) apparatus, and particularly to an X-ray CT apparatus for use preferably for cardiac function diagnosis, a method for controlling the apparatus and a method for generating images by using the apparatus.
An X-ray CT apparatus is provided, as shown in FIG. 4, with a scanner gantry section 10 for performing radiation and detection of R-rays, a data processing section 20 for processing measurement data detected by the scanner gantry section 10 into a CT image signal, and a display unit 30 for displaying the CT image. The scanner gantry section 10 is provided with a rotary disc 11, an opening portion 14 formed in the rotary disc 11, an X-ray tube 12 mounted on the rotary disc 11, an X-ray detector 15 attached so as to face the X-ray tube 12, and a detector circuit 16 for converting an output signal of the X-ray detector 15 into a digital signal S1. The rotary disc 11 is designed so as to rotate around an object 18 laid down on a bed (not shown) disposed in the opening portion 14 while the X-rays are radiated onto one sliced section of the object 18. As a result of one scan, one slice image can be obtained by one scan. If such a scan is repeated by a plurality of times while the position of the rotary disc 11 relative to the object 18 is being changed, data of a plurality of images can be obtained with respect to a desired image pick-up portion. The rotation of the rotary disc 11 and the width of X-ray flux are controlled by a scanner gantry control circuit 17.
As the scan method for obtaining CT images, there are a full scan method in which one scan is completed by making an X-ray source rotate around an object by 360 degrees and a half scan method in which scan is completed by X-ray movement by about 210xcx9c240 degrees. In the full scan method, generally, image pick up is carried out in a time of one to several seconds per scan.
In the data processing section 20, on the other hand, a digital signal Sl is sent to a CT image operation section 21 from the detector circuit 16 at every scan. Operation such as arrangement processing, filtering processing, reverse projection processing, etc. are performed in the CT image operation section 21, so that image data are generated with respective to the sliced section. Attribute information relating to the images is added to the image data in an image information adding section 22. The image data are processed into a display signal in a display circuit section 24. Slice images are displayed on a display unit 30.
There is also such a CT apparatus in which a three-dimensional image generating section is provided (between the image information adding section 22 and the display circuit section 24) in the data processing section so that three-dimensional information is extracted from a series of CT images to thereby display three-dimensional CT images. In this case, data of a plurality of tomography images obtained by a plurality of scans are reconstituted into three-dimensional image data.
Two-dimensional sectional images in the direction of a body axis of the object crossing the sliced face in the scanning direction, such as sagittal images or coronal images, can be obtained in a manner in which only data components of a specific plane parallel with a body axis are extracted out of three-dimensional image data, and two-dimensional images of the plane are reconstructed on the basis of the extracted data components. Three-dimensional images can be obtained in a manner in which data components of specific three-dimensional coordinates are extracted out of three-dimensional image data, and three-dimensional images are reconstructed on the basis of the extracted data components.
The sagittal images, coronal images and three-dimensional tomography images can be obtained by means of computer graphics technique disclosed in the xe2x80x9cThree Dimensional Processing For Computer Tomography Imagesxe2x80x9d described in the magazine titled xe2x80x9cPIXELxe2x80x9d, Vol. 16, pp. 28-35, 1984, 1.
In a case of performing cardiac image-diagnosis by using such an X-ray CT apparatus, image distortion due to cardiac pulsation occurs in the CT images. Particularly in the case of a plurality of CT images which are different in measurement time from each other, the images are not coincident with each other in pulsation phase so that the image distortion increases in the three-dimensional images or in the reconstructed sagittal (or coronal) images to lose values of diagnosis. In order to avoid this disadvantage, there has been proposed a method (ECG gated CT image reconstituting method) in which image operation is carried out by collecting only data measured from the measurement data by a plurality of scans at a predetermined phase of the electrocardiographic complex. In this method, however, since only specific measurement data are used among a large number of measurement data, there is a disadvantage that image noise due to shortage of the quantity of data becomes large or the time for test and the quantity of use of a contrast medium increase because the number of scans is increased so as to make the SN ratio large.
In the conventional X-ray CT apparatus, the rotational speed of the rotary disc, that is, the scan speed has no connection with the period of the cardiac pulsation of a object and scan is performed at a constant speed. Accordingly, among a plurality of slice images which are different in measurement time from each other, the images are not coincident in phase of pulsation with each other so that distortion appears in cardiac sagittal or coronal images or cardiac three-dimensional images to make the diagnosis difficult.
It is therefore an object of the present invention to provide an X-ray CT apparatus in which slice images or three-dimensional images of a moving object can be reconstructed without any distortion and to provide a control method therefor.
It is another object of the present invention to provide an X-ray CT apparatus in which sagittal or coronal images, or three-dimensional images effective for diagnosis of a heart or any other organ can be clearly reconstructed without increasing the time taken for examination and the quantity of use of a contrast medium, and to provide a control method therefor.
It is a further object of the present invention to provide a method in which slice images or three-dimensional images of a object can be reconstructed by controlling the scan speed synchronously with an electro-cardiogram of the object.
The X-ray CT apparatus, the control method therefor, and the image generating method according to the present invention commonly have a technical subject matter that an outside signal corresponding to movement of an object to be inspected or a living body is received from the outside of a scan controller and the scan speed is controlled synchronously with the outside signal.
According to an aspect of the present invention, an X-ray computerized tomography apparatus comprises: an X-ray generating source for irradiating an object with X-rays; means for detecting X-rays transmitted through the object; a scan means for controlling direction of irradiation with X-rays so that a periphery of the object is scanned in a predetermined direction with the X-rays from the-X-ray generating source; and a control means for controlling a scan speed of the scan means on the basis of an external signal synchronized with movement of a part or whole of the object.
According to another aspect of the present invention, an X-ray computerized tomography apparatus comprises: a rotary member on which an X-ray source and an X-ray detector are disposed so as to be opposite to each other with respect to a center of rotation of the rotary member; an opening portion provided so that a object can be arranged on the center of rotation of the rotary member; a scan control section for controlling drive of the X-ray source and the rotary member so that the rotary member rotates to thereby perform scan on the periphery of the object with the X-rays in a direction of a sliced face crossing a body axis of the object; an image reconstituting section for generating a slice image signal of the object on the basis of an output signal of the X-ray detector obtained during the scan; a display unit for displaying a slice image of the object on the basis of the slice image signal; and a scan speed control section for receiving an electrocardiogram signal of the object to thereby control a rotational speed of the rotary member on the basis of the electrocardiogram signal.
According to a further aspect of the present invention, an image generating method by using an X-ray computerized tomography apparatus, comprises the steps of: scanning a object with X-rays along a sliced face crossing a body axis of the object while an irradiation source of the X-rays is rotated around the object; changing relative positions of the object and the irradiating source along the direction of the body axis and repeating the step of scanning the object with the X-rays every time the relative positions are changed; receiving an electrocardiogram signal of the object and controlling a scan speed of the X-rays synchronously with a period of the electrocardiogram signal; detecting the X-rays transmitted through the object every time the scan is performed to thereby collect image information with respect to a sliced face of the object; and generating three-dimensional image information of the object on the basis of image information collected by scan on a plurality of different sliced faces.